Anaerobic Respiration and Alternative Respiratory Substrates

• 4 ATP produced gross, 2 ATP produced net
• Pacts as the final electron acceptor instead of oxygen
• In animals - pyruvate becomes reduced and accepts the hydrogen from NADH forming lactate

  
  

  In yeast and higher plants - pyruvate is decarboxylated to ethanal, which then accepts the hydrogen from NADH forming ethanol
• When carbohydrate levels are low, lipids are used as a respiratory substrate. Lipids contain twice as much energy per unit gram as carbohydrates
• Lipids are hydrolysed, breaking the ester bond and forming glycerol and 3 fatty acid chains.
• The glycerol is phosphorylated by ATP, and dehydrogenated and converted into triose phosphate, which can enter glycolysis
• The fatty acid chains are split into 2 carbon acetate fragments, which enter the krebs cycle as acetyl co-enzyme A
• Proteins can also be used as a respiratory substrate, usually after reserves of carbohydrates and lipids have been used up. First the proteins are hydrolysed into amino acids. They are then deaminated in the liver. leaving behind a keto acid, which can be inserted into glycolysis or the krebs cycle as alpha-ketoglutarate